Polymer-diluent mixtures concentration

It has long been a mystery why diffusion coefficients of polymer-diluent systems, especially when the diluent is a good solvent for a given polymer, exhibit so pronounced a concentration dependence that it looks extraordinary. Several proposals have been made for the interpretation of this dependence. Thus Park (1950) attempted to explain it in terms of the thermodynamic non-ideality of polymer-diluent mixtures, but it was found that such an effect was too small to account for the actual data. Fujita (1953) suggested immobilization of penetrant molecules in the polymer network, which, however, was not accepted by subsequent workers. Recently, Barrer and Fergusson (1958) reported that their diffusion coefficient data for benzene in rubber could be analyzed in terms of the zone theory of diffusion due to Barrer (1957). Examination shows, however, that their conclusion is never definitive, since it resorted to a less plausible choice of the value for a certain basic parameter. 

The molecular weight between entanglements of a homogeneous polymer-diluent mixture in which the concentration of diluent is 0.15 g/cm is 20,000 g/mol. Make a rough estimation of the solvent that should be added to 100 cm of the mixture to give a molecular weight between entanglements of 25,000 g/mol. 

Gibbs and DiMarzio (1958) appear to have been the first to offer a molecular interpretation, via statistical mechanics, of the depression of glass transition temperature (Tg) of an amorphous polymer by the addition of low-molecular-weight soluble diluents, in terms of the size and stiffness of diluents and the diluent concentration. Subsequently, using both classical and statistical thermodynamics, Chow (1980) derived the following expression, which predicts the T depression of polymer/diluent mixtures ... 

DVB were valid in this system as well. These concern the dependence of surface area and pore volume on the amount of diluent and cross-linker. The surface area increases with the amount of EDMA and goes through a maximum with increasing amount of diluent. Using cyclohexanol-dodecanol as a solvent-non-solvent pair, the factors of importance for the structure and morphology of the polymers were studied by experimental design [34]. In these experiments the concentration of the diluent mixture was varied between 20 and 77% (volume/total volume), the concentration of EDMA between 25 and 100% (volume/monomer volume), the concentration of initiator (AIBN) between 0.2 and 4% (w/w), the concentration of non-solvent (dodecanol), between 0 and 15% (v/v) and the polymerisation temperature between 70° and 90°C. The surface area (determined by nitrogen sorption), pore volume (determined by mercury porosimetry) (see Section 2.11.6.) and the mechanical properties were chosen as responses. 

From these values, one may calculate and compare the effective glass transition temperature of the resin as a function of diluent concentration. Gordon et a1. have recently derived an expression relating the glass temperature of a polymer-plasticizer mixture to the glass temperatures of the components on the basis of the configurational entropy theory of glass formation (4). 

In analyzing polyethylene-diluent mixtures it was noted that for certain diluents and concentrations the melting temperature remained invariant with composition. This is not an isolated observation. Besides linear polyethylene, this phenomenon has also been observed in long chain branched polyethylene,(21) poly(chlorotrifluoroethylene),(22) poly(N,N -sebacoyl piperazene),(23) isotactic poly(propylene),(24) and poly (acrylonitrile) (25) when the polymers are admixed... 

Potentially very explosive, it may be handled and transferred by low temperature distillation. It should be stored at —25°C to prevent decomposition and formation of explosive polymers [1]. The critical pressure for explosion is 0.04 bar, but presence of 15-40% of diluents (acetylene, ammonia, carbon dioxide or nitrogen) will raise the critical pressure to 0.92 bar [2], Further data on attenuation by inert diluents of the explosive decomposition of the diyne are available [3], During investigation of the cause of a violent explosion in a plant for separation of higher acetylenes, the most important finding was to keep the concentration of 1,3-butadiyne below 12% in its mixtures. Methanol is a practical diluent [4], The use of butane (at 70 mol%) or other diluents to prevent explosion of 1,3-butadiyne when heated under pressure has been claimed [5], It polymerises rapidly above 0°C. 

Bueche (16,172) proposed that the viscosity is proportional to the fourth power of the polymer concentration and a complex function of the free volume of the mixture. Kraus and Gruver (170) find that the 3.4 power fits experimental data better than does the fourth power. They used equation (58) with (r2) replaced by the mean-square radius of gyration (s2). The term r2)/(rf) indicates that poor solvents should lower the viscosity more than a good solvent. As the temperature increases, the factor increases as a function of the ratio (T - 7 (tJJ)/(7 - 7 ). The glass transition temperatures of the polymer and diluent are andT o, respectively. 

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